1. Field of the Invention
The present invention relates to an apparatus for measuring the weight of a vehicle seat including the weight of a passenger sitting thereon and, more particularly, to a seat weight measuring apparatus which is improved to have higher precision in measuring the weight of a passenger sitting on a vehicle seat. Further, it relates to a seat weight measuring apparatus capable of detecting the center of gravity of a passenger with a smaller number of load cells.
2. Description of the Related Art
Automobiles are equipped with seat belts and airbags to secure safety for passengers. In recent years, there is a trend for controlling the operation of such safety devices according to the weight (body weight) and/or posture of a passenger for improved performance of seat belts and airbags. For example, the amount of gas to be introduced into the airbag, an airbag inflating speed, or a pre-tension of the seat belt may be adjusted according to the weight and/or posture of a passenger. For that purpose, some means are needed for measuring the weight of the passenger sitting on the seat. In addition, for estimating the posture of the passenger, the position of the center of gravity of the passenger on the seat can be referred.
An example of such means includes a proposal (Japanese Patent Applications No. 9-156666, No. 10-121627, and the like filed by the applicant of this invention) which involves arranging load sensors (load cells) at four corners of the seat under seat rails and summing vertical loads acting on the load cells to know the weight and the center of gravity of the passenger. According to the proposed method, the position of the center of gravity of the passenger on the seat can be also obtained.
However, since such seat weight measuring apparatuses are installed in general motor vehicles, these must be manufactured at low cost. Further, these must be easily wired and easily assembled. It is necessary for accurate measuring to exclude other load than the weight of a seat and the weight of a passenger (or an object) on the seat.